As evidenced by U.S. Pat. Nos. 3,724,332 and 3,728,942, it is known that the movement of a spool valve in a hydraulic brake booster can be limited so as to provide a pressure limiter for the pressurized fluid within a pressure chamber. The control valve is movable within a bore in the housing to open an inlet port to the pressure chamber while at the same time closing an outlet port so that pressurized fluid communicated to the pressure chamber is increased. If the level of pressure within the pressure chamber reaches a predetermined value, the pressure limiter is activated to prohibit further increases in the pressure level.